the formation of vegetable mould-第14节

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and　Dr。　King；　who　looked　carefully；　never　saw　even　a　fragment　of　a　
leaf　thus　drawn　in。　　Nor　could　any　trace　be　discovered　of　the　worms　
having　crawled　down　the　exterior　surfaces　of　the　towers　in　search　
of　leaves；　and　had　they　done　so；　tracks　would　almost　certainly　have　
been　left　on　the　upper　part　whilst　it　remained　soft。　　It　does　not；　
however；　follow　that　these　worms　do　not　draw　leaves　into　their　
burrows　during　some　other　season　of　the　year；　at　which　time　they　
would　not　build　up　their　towers。

From　the　several　foregoing　cases；　it　can　hardly　be　doubted　that　
worms　swallow　earth；　not　only　for　the　sake　of　making　their　burrows；　
but　for　obtaining　food。　　Hensen；　however；　concludes　from　his　
analyses　of　mould　that　worms　probably　could　not　live　on　ordinary　
vegetable　mould；　though　he　admits　that　they　might　be　nourished　to　
some　extent　by　leaf…mould。　｛39｝　　But　we　have　seen　that　worms　
eagerly　devour　raw　meat；　fat；　and　dead　worms；　and　ordinary　mould　
can　hardly　fail　to　contain　many　ova；　larvae；　and　small　living　or　
dead　creatures；　spores　of　cryptogamic　plants；　and　micrococci；　such　
as　those　which　give　rise　to　saltpetre。　　These　various　organisms；　
together　with　some　cellulose　from　any　leaves　and　roots　not　utterly　
decayed；　might　well　account　for　such　large　quantities　of　mould　
being　swallowed　by　worms。　　It　may　be　worth　while　here　to　recall　the　
fact　that　certain　species　of　Utricularia；　which　grow　in　damp　places　
in　the　tropics；　possess　bladders　beautifully　constructed　for　
catching　minute　subterranean　animals；　and　these　traps　would　not　
have　been　developed　unless　many　small　animals　inhabited　such　soil。

The　depth　to　which　worms　penetrate；　and　the　construction　of　their　
burrows。Although　worms　usually　live　near　the　surface；　yet　they　
burrow　to　a　considerable　depth　during　long…continued　dry　weather　
and　severe　cold。　　In　Scandinavia；　according　to　Eisen；　and　in　
Scotland；　according　to　Mr。　Lindsay　Carnagie；　the　burrows　run　down　
to　a　depth　of　from　7　to　8　feet；　in　North　Germany；　according　to　
Hoffmeister；　from　6　to　8　feet；　but　Hensen　says；　from　3　to　6　feet。　　
This　latter　observer　has　seen　worms　frozen　at　a　depth　of　1。5　feet　
beneath　the　surface。　　I　have　not　myself　had　many　opportunities　for　
observation；　but　I　have　often　met　with　worms　at　depths　of　3　to　4　
feet。　　In　a　bed　of　fine　sand　overlying　the　chalk；　which　had　never　
been　disturbed；　a　worm　was　cut　into　two　at　55　inches；　and　another　
was　found　here　at　Down　in　December　at　the　bottom　of　its　burrow；　at　
61　inches　beneath　the　surface。　　Lastly；　in　earth　near　an　old　Roman　
Villa；　which　had　not　been　disturbed　for　many　centuries；　a　worm　was　
met　with　at　a　depth　of　66　inches；　and　this　was　in　the　middle　of　
August。

The　burrows　run　down　perpendicularly；　or　more　commonly　a　little　
obliquely。　　They　are　said　sometimes　to　branch；　but　as　far　as　I　have　
seen　this　does　not　occur；　except　in　recently　dug　ground　and　near　
the　surface。　　They　are　generally；　or　as　I　believe　invariably；　lined　
with　a　thin　layer　of　fine；　dark…coloured　earth　voided　by　the　worms；　
so　that　they　must　at　first　be　made　a　little　wider　than　their　
ultimate　diameter。　　I　have　seen　several　burrows　in　undisturbed　sand　
thus　lined　at　a　depth　of　4　ft。　6　in。；　and　others　close　to　the　
surface　thus　lined　in　recently　dug　ground。　　The　walls　of　fresh　
burrows　are　often　dotted　with　little　globular　pellets　of　voided　
earth；　still　soft　and　viscid；　and　these；　as　it　appears；　are　spread　
out　on　all　sides　by　the　worm　as　it　travels　up　or　down　its　burrow。　　
The　lining　thus　formed　becomes　very　compact　and　smooth　when　nearly　
dry；　and　closely　fits　the　worm's　body。　　The　minute　reflexed　
bristles　which　project　in　rows　on　all　sides　from　the　body；　thus　
have　excellent　points　of　support；　and　the　burrow　is　rendered　well　
adapted　for　the　rapid　movement　of　the　animal。　　The　lining　appears　
also　to　strengthen　the　walls；　and　perhaps　saves　the　worm's　body　
from　being　scratched。　　I　think　so　because　several　burrows　which　
passed　through　a　layer　of　sifted　coal…cinders；　spread　over　turf　to　
a　thickness　of　1。5　inch；　had　been　thus　lined　to　an　unusual　
thickness。　　In　this　case　the　worms；　judging　from　the　castings；　had　
pushed　the　cinders　away　on　all　sides　and　had　not　swallowed　any　of　
them。　　In　another　place；　burrows　similarly　lined；　passed　through　a　
layer　of　coarse　coal…cinders；　3。5　inches　in　thickness。　　We　thus　see　
that　the　burrows　are　not　mere　excavations；　but　may　rather　be　
compared　with　tunnels　lined　with　cement。

The　mouths　of　the　burrow　are　in　addition　often　lined　with　leaves；　
and　this　is　an　instinct　distinct　from　that　of　plugging　them　up；　and　
does　not　appear　to　have　been　hitherto　noticed。　　Many　leaves　of　the　
Scotch…fir　or　pine　（Pinus　sylvestris）　were　given　to　worms　kept　in　
confinement　in　two　pots；　and　when　after　several　weeks　the　earth　was　
carefully　broken　up；　the　upper　parts　of　three　oblique　burrows　were　
found　surrounded　for　lengths　of　7；　4；　and　3。5　inches　with　pine…
leaves；　together　with　fragments　of　other　leaves　which　had　been　
given　the　worms　as　food。　　Glass　beads　and　bits　of　tile；　which　had　
been　strewed　on　the　surface　of　the　soil；　were　stuck　into　the　
interstices　between　the　pine…leaves；　and　these　interstices　were　
likewise　plastered　with　the　viscid　castings　voided　by　the　worms。　　
The　structures　thus　formed　cohered　so　well；　that　I　succeeded　in　
removing　one　with　only　a　little　earth　adhering　to　it。　　It　consisted　
of　a　slightly　curved　cylindrical　case；　the　interior　of　which　could　
be　seen　through　holes　in　the　sides　and　at　either　end。　　The　pine…
leaves　had　all　been　drawn　in　by　their　bases；　and　the　sharp　points　
of　the　needles　had　been　pressed　into　the　lining　of　voided　earth。　　
Had　this　not　been　effectually　done；　the　sharp　points　would　have　
prevented　the　retreat　of　the　worms　into　their　burrows；　and　these　
structures　would　have　resembled　traps　armed　with　converging　points　
of　wire；　rendering　the　ingress　of　an　animal　easy　and　its　egress　
difficult　or　impossible。　　The　skill　shown　by　these　worms　is　
noteworthy　and　is　the　more　remarkable；　as　the　Scotch　pine　is　not　a　
native　of　this　district。

After　having　examined　these　burrows　made　by　worms　in　confinement；　I　
looked　at　those　in　a　flower…bed　near　some　Scotch　pines。　　These　had　
all　been　plugged　up　in　the　ordinary　manner　with　the　leaves　of　this　
tree；　drawn　in　for　a　length　of　from　1　to　1。5　inch；　but　the　mouths　
of　many　of　them　were　likewise　lined　with　them；　mingled　with　
fragments　of　other　kinds　of　leaves；　drawn　in　to　a　depth　of　4　or　5　
inches。　　Worms　often　remain；　as　formerly　stated；　for　a　long　time　
close　to　the　mouths　of　their　burrows；　apparently　for　warmth；　and　
the　basket…like　structures　formed　of　leaves　would　keep　their　bodies　
from　coming　into　close　contact　with　the　cold　damp　earth。　　That　they　
habitually　rested　on　the　pine…leaves；　was　rendered　probable　by　
their　clean　and　almost　polished　surfaces。

The　burrows　which　run　far　down　into　the　ground；　generally；　or　at　
least　often；　terminate　in　a　little　enlargement　or　chamber。　　Here；　
according　to　Hoffmeister；　one　or　several　worms　pass　the　winter　
rolled　up　into　a　ball。　　Mr。　Lindsay　Carnagie　informed　me　（1838）　
that　he　had　examined　many　burrows　over　a　stone…quarry　in　Scotland；　
where　the　overlying　boulder…clay　and　mould　had　recently　been　
cleared　away；　and　a　little　vertical　cliff　thus　left。　　In　several　
cases　the　same　burrow　was　a　little　enlarged　at　two　or　three　points　
one　beneath　the　other；　and　all　the　burrows　terminated　in　a　rather　
large　chamber；　at　a　depth　of　7　or　8　feet　from　the　surface。　　These　
chambers　contained　many　small　sharp　bits　of　stone　and　husks　of　
flax…seeds。　　They　must　also　have　contained　living　seeds；　for　on　the　
following　spring　Mr。　Carnagie　saw　grass…plants　sprouting　out　of　
some　of　the　intersected　chambers。　　I　found　at　Abinger　in　Surrey　two　
burrows　terminating　in　similar　chambers　at　a　depth　of　36　and　41　
inches；　and　these　were　lined　or　paved　with　little　pebbles；　about　as　
large　as　mustard　seeds；　and　in　one　of　the　chambers　there　was　a　
decayed　oat…grain；　with　its　husk。　　Hensen　likewise　states　that　the　
bottoms　of　the　burrows　are　lined　with　little　stones；　and　where　
these　could　not　be　procured；　seeds；　apparently　of　the　pear；　had　
been　used；　as　many　as　fifteen　having　been　carried　down　into　a　
single　burrow；　one　of　which　had　germinated。　｛40｝　　We　thus　see　how　
easily　a　botanist　might　be　deceived　who　wished　to　learn　how　long　
deeply　buried　seeds　remained　alive；　if　he　were　to　collect　earth　
from　a　considerable　depth；　on　the　supposition　that　it　could　contain　
only　seeds　which　had　long　lain　buried。　　It　is　probable　that　the　
little　stones；　as　well　as　the　seeds；　are　carried　down　from　the　
surface　by　being　swallowed；　for　a　surprising　number　of　glass　beads；　
bits　of　tile　and　of　glass　were　certainly　thus　carried　down　by　worms　
kept　in　pots；　but　some　may　have　been　carried　down　within　their　
mouths。　　The　sole　conjecture　which　I　can　form　why　worms　line　their　
winter…quarters　with　little　stones　and　seeds；　is　to　prevent　their　
closely　coiled…up　bodies　from　coming　into　close　contact　with　the　
surrounding　cold　soil；　and　such　contact　would　perhaps　interfere　
with　their　respiration　which　is　effected　by　the　skin　alone。

A　worm